1. Field of the Invention
The present invention relates to fire rated electronic door locks that have components made of plastic or other materials having a relatively low ignition temperature. More specifically, the present invention relates to a fire rated electronic door lock that includes a mechanism, actuated by the heat of a fire on the hot side of a fire door, which acts to disconnect wiring from lock components mounted on the cold side of the fire door. By disconnecting wiring from the cold side, the cold side lock components are no longer tethered with wiring to the fire door and can drop away to prevent ignition and improve fire resistance.
2. Description of Related Art
Electronic door locks typically include lock components mounted in housings on opposite sides of the door. These lock components may include card readers, proximity detectors, keypads, LED and LCD displays and indicators, batteries, printed circuit board assemblies, actuators and the like. Many of these electronic lock components incorporate materials made of plastic.
Often the lock housings and escutcheons are made of metal. It would be highly desirable to have the option to make the housings and escutcheons out of plastic instead of metal to reduce cost and increase design flexibility.
A problem with the use of plastic for the housing and with plastic found in common off-the-shelf electronic components is the relatively low ignition temperature of these materials. Many types of plastic will eventually begin to burn if they are exposed to sufficiently high temperatures.
For a fire door, the side of the door exposed to the fire may be referred to as the “hot” side and the opposite side may be referred to as the “cold” side. In order to meet applicable fire codes and standards, a fire rated door and the locks installed thereon must withstand exposure to a fire for a relatively long period of time without allowing the fire to pass through the door.
Although the “cold” side of the fire door is not directly exposed to an open flame during fire rating tests, it is slowly heated to a very high temperature during testing as the heat of the fire on the hot side passes through the fire door. Fire rated doors are most commonly made of metal and the temperature of the fire door on the “cold” side will typically exceed 1000° F. (538° C.) during testing. To meet certain fire test standards, the lock components on the cold side must withstand three hours of exposure to this high temperature without ignition. It is very difficult to meet this standard when the lock components on the cold side are made of plastic.
The high temperature on the cold side easily exceeds the melting and ignition temperatures of many common materials, such as plastics. Due to lower cost and greater design flexibility, plastics would be desirable for use in constructing the lock housing if not for the ignition risk of such materials. The potential for undesirable ignition also limits the design and use of other components in electronic locks, such as common electronic components and mechanical components. As a result, in order to meet fire rating standards for electronic locks installed on fire doors, it has heretofore been necessary to construct the lock housing of metal or other relatively expensive non-flammable, high ignition temperature materials.
The non-flammable housing acts to contain the electrical and other potentially flammable components used in the electronic lock and prevents them from igniting or producing an open flame, which would allow passage of the fire through the fire door. Even with a metal housing, the lock designer is often limited in the choice and positioning of components made of plastic. Although limited amounts of plastic may be used inside the metal housing, it has not previously been possible to make the housing of plastic or to use significant amounts of plastic and other low ignition temperature materials. If such materials are used for the lock housing on the “cold” side of a fire door, there is a significant risk that the heat of the fire will eventually melt and ignite such materials. Ignition of lock components on the “cold” side during fire testing results in failure of the fire certification process.
One method of preventing such ignition is to physically separate the lock components from the surface of the fire door before the ignition temperature is released. This requires, at a minimum, that any mechanical mounting of the lock mechanism to the cold side door surface be released when the fire door is exposed to fire on the hot side so that the lock mechanism can drop away from the heated fire door.
The mechanical mount may be mounting screws, studs, tabs, etc. Typically the lock mechanism will include a mounting plate that is bolted to the cold side of the fire door. A circuit board and the electrical components will be mounted within a housing attached to the base plate. In order to use low ignition temperature materials, such as a plastic housing, it would be desirable to release the housing and circuit board and/or to release the mounting plate during a fire so that all components on the cold side that can be ignited will fall away from the heated fire door before they reach ignition temperature.
For electronic locks, however, it is not sufficient merely to disconnect the mechanical lock mounting. Electronic locks include a circuit board and/or other components of the lock that are electrically connected to the rest of the lock system. The electrical connections are typically made with copper wires, such as a ribbon cable or with individual wires. Copper has a relatively high melting point. The electrical wires act to tether the lock mechanism and form an additional mechanical connection between the lock mechanism and the fire door. This additional connection must also be released if the lock mechanism is to be allowed to drop away and physically separate from the fire door.
A need exists in the art for improved electronic door lock designs that are fire rated wherein lower cost materials, such as various types of plastic, can be used for the housing and used in greater quantities for other lock components. Plastics and other compounds having a relatively low ignition temperature can provide more flexible design options than metal.
The term “low ignition temperature” as used herein refers to a sufficiently low ignition temperature that there is a significant risk of ignition when the material is exposed to heat on the cold side of a fire door during fire testing in which the heat from a fire is applied to the hot side of the fire door.
Even if metal is used in the housing on one side of the fire door, the components on the other side must withstand the heat of the fire. Both sides of the lock mechanism must prevent passage of the fire through the fire door as a fire can occur on either side.
Because plastics are widely used in electronic components, such as in sensors, relays, connectors, integrated circuit packaging and the like, an electronic lock design which separates the lock from the fire door during a fire allows greater quantities of plastic to be used, such as in card readers, proximity sensors, motor housings, display indicators, etc. without risk of ignition.
It will be noted that the terms “door lock” and “lock mechanism” and the like, as used herein, refer to the electronic control portion of a door lock or other door hardware intended to be mounted on a fire door. The door lock mechanism may include keypads, proximity detectors, card readers, display lights, batteries, printed circuit board assemblies, control systems for reporting events to a central lock system, wireless transmitters, receivers and the like, all of which are mounted on a fire door in a housing. All of these electronic components are included within the scope of the terms “door lock” and “lock mechanism” and the like as used herein.
Conventional mechanical door lock components, such as handles, pushbars, key cylinders, turn knobs, latch bolts, dead bolts, guard bolts, locking assemblies, etc. may all be separate from the door lock mechanism referred to here. The door lock mechanism of this invention may control a mortise lock, cylindrical lock, bored lock, exit device or other fire door hardware and may be integrated therewith or may be completely separate therefrom.
Generally, the mechanical hardware will not present a fire risk as it will be made of metal. Thus, as used herein, the terms above referring to the lock may be interpreted to include only some of the electronic components that control or are mounted with other mechanical lock components.